This invention relates to the manufacture of gas turbine blades or buckets and specifically, to an internal core arrangement utilized in the casting of turbine buckets, and to a bucket having cooling inlet passages formed by the core.
Single five-pass aft-flowing serpentine circuits have been proven to be an efficient and cost effective means of air cooling the shank and airfoil portions of a gas turbine bucket. This design represented a step forward in turbine cooling technology since air cooled stage 2 buckets have historically been cooled by stem-drilled radial holes. Since the source of the coolant air for the serpentine circuit is at the bottom or radially inner end of the dovetail mounting portion of the bucket, a passage is provided for feeding air through the shank portion of the bucket. In the prior arrangement, the cast inlet passage to the serpentine circuit is large and fills most of the shank in order to minimize the amount of solid metal in the shank. Weight minimization is important since extra weight increases the centrifugal loading on the rotor wheel. The problem with this prior design, however, is the lack of a continuous rib along the entire length of the bucket including the shank and airfoil portions, which is an important mechanical design criteria for bucket stiffness.
Another core arrangement, is disclosed in copending application Ser. No. 10/604,220, filed Jul. 1, 2003. This so-called “pant-leg” core is used in certain stem cooled buckets but like the core discussed above, it does not allow for a continuous center rib from the dovetail mounting portion to the bucket tip.